1. Field of the Invention
Embodiments of the present invention generally relate to joint color channel image noise filtering and edge enhancement of digital images in the Bayer domain.
2. Description of the Related Art
Images (i.e., single photographs or frames/pictures in video sequences) captured by imaging sensors in digital cameras often contain large amounts of random noise that degrades image quality. Typically, one or more image noise filters are applied to the captured images at various points (e.g., in the Bayer domain and/or the YUV domain) during the processing of the images to reduce the noise and improve visual quality.
An image is processed by many components in an image pipe before it is converted to the YUV domain. These processing components may change the noise characteristics drastically, e.g., noise from one color channel may leak to another color channel, thus making noise removal much more difficult. A Bayer domain noise filter is applied to an image before processing by other components in the image pipe, i.e., before the processing by the other components possibly changes the noise characteristics in the image. Thus, application of noise filtering and edge enhancement in the Bayer domain may be better than application in the YUV domain. Further, if noise is removed in the Bayer domain, the performance of the other components in the image pipe may be more robust as they would receive less noisy and sharper inputs.
A Bayer domain noise filter is also more effective at removing low-frequency noise that a YUV domain filter. The width and height of the Bayer image in each color channel are just half of the width and height of the YUV image. If the same filter is applied in the Bayer domain and the YUV domain, the effective filter size in the Bayer domain is twice that of the filter size in YUV domain. The larger effective filter size in Bayer domain can thus remove noise with lower frequency.